IFilter

An IFilter is a plugin that allows Microsoft's search engines to index various file formats (as documents, email attachments, database records, audio metadata etc.) so that they become searchable. Without an appropriate IFilter, contents of a file cannot be parsed and indexed by the search engine.

Contents

An IFilter acts as a plug-in for extracting full-text and metadata for search engines. A search engine usually works in two steps:

The search engine goes through a designated place, e.g. a file folder or a database, and indexes all documents or newly modified documents, including the various types documents, in the background and creates internal data to store indexing result.

A user specifies some keywords he would like to search and the search engine answers the query immediately by looking up the indexing result and responds to the user with all the documents that contains the keywords.

During Step 1, the search engine itself doesn't understand format of a document. Therefore, it looks on Windows registry for an appropriate IFilter to extract the data from the document format, filtering out embedded formatting and any other non-textual data.